Electrical ignition system



April 2, 1946. M. w. G. CHITTY 2,397,725

ELECTRICAL IGNITION SYSTEM Filed'Jan. 15, 1945 FIG 1.

Patented Apr. 2, 1946 UNITED STATES TENT orFrcE I 2,397,725 ELECTRICAL rem'rron sys'rEM Application January 13, 1943, Serial No. 472,263

In Great Britain January 13, 1942 6 Claims.

This invention relates to electrical ignition systems and has for its object to provide reliable ignition for internal combustion engines and in particular to enable standard magnetos to be adapted for the purpose of providing an output voltage having a very steep wave front which has been found advantageous in aflording the ability to operate satisfactorily when a large leakage conductance is connected across the output of the apparatus and also when the air density of the surrounding atmosphere is very low.

I have found that the armature inductance of a magneto of usual construction is too Great to allow satisfactory operation over the wide range of speed encountered in a modern aero engine, when the armature coil is connected in parallel with the condenser and operated as an alternator to charge the condenser and that complications arise when as in the case of a magneto the surge alternates in polarity. However satisfactory results are obtainable according to the invention with an arrangement in which a source of energy such as the armature coil of the magneto is used to charge a condenser to about 300 volts and discharge it through a step-up transformer whose output is connected through a distributor to the spark plugs by breaking a current in the armature coil and using the voltage surge so produced to charge the condenser through a rectifier in the manner hereinafter more fully described by reference to the accompanying drawing in which:

Fig. 1 shows a useful form of a circuit which I have found to be more efficient and more economical in rectifier space than conventional full wave circuits, and

Fig. 2 represents a useful alternative thereof.

In Fig. 1 L is the armature coil of the magneto, A and B are contact makers operated through a cam keyed to the main rotor shaft of the magneto, C the condenser and T the step-up transformer for the primary P and secondary S, the latter being connected through the usual distributor to the sparking plugs of the engine.

When both contact mak'ers A and B are closed by rotation of the magneto shaft 9. current builds up in the circuit containing the armature coil L and the rectifiers R1, R2. Contact maker A then opens, B remaining closed allowing a surge to pass from the coil through rectifier R1 into the condenser C which does not discharge when the tributor of normal construction. Contact makers A and B are now closed and current again builds up in L but this time of opposite poiarityto the Now contact maker B opens and the condenser is charged through rectifier R2, B then closes and the condenser is discharged into transformer T.

In order to guard against any possible loss in the rectifiers by limiting the current build up in L a contact breaker may be added across L if desired. However, the system has been successfully employed using the circuit as described which is more readily applicable to the simple alteration of a' standard magneto to give a high frequency discharge.

In the arrangement according to Fig. 1 the contact makers A and B have to perform a dual function in that in addition to having to break.

the current in the armature coil, thus giving rise to the charging of the condenser, they have to perform their principal operation, 1. e. that of discharging the condenser when charged into the ever of the single condenser C in Fig. 1 provision is made of two separate condensers C1 and C2 of equal value.

When contact maker A is open condenser Cl. is charged up by the alternator voltage of L through rectifier R1. When C1 is charged A then closes discharging C1 into the step-up transformer 'I. Now contact maker B opens, condenser C2 is charged through rectifier R2 and when B closes discharges into transformer '1.

However, considering C1 charged, to avoid condenser Cz shunting transformer 'I' when A closes, contact maker B opens just before A closes. Similarly A opens Just before B closes. Thus it will be seen that no current change is effected by the opening of A or B. r

The values of L and C and C1 and C2 respectively are adjusted such that while adequate low speed operation is obtained the voltage surge obtained from L at high speed is of such a slop-- ing wave front that the requisite condenser is discharged by the operative contact maker before the peak of the wave is reached. This gives a good measure of regulation to the system.

With advantage the transformer T is wound on a small insulating former or a laminated iron core and enclosed in a container of insulating in the coil due to corona which is very considerable in a magneto armature coil of normal construction.

It may be noted that the altitude limit is determined by flash over in the distributor and it may be found desirable to distribute the condenser discharge into the primary of a series of transformers whose output is directly connected to the plugs through screen cables.

The rectiflers may be of the mercury vapour or copper oxide or selenium type the latter being preferred as being more resistant to vibration and shock as well as being more economical of space. A fan may be used if convenient to provide some cooling for the rectiflers. The fan may be arranged on the main rotor shaft to advantage.

The advantage of this system over other high frequency systems lies in the ability to operate for a longer life than a system using spark gaps or discharge tubes and also to provide more accurate timing as the discharge takes place only when the'contact makers, which are mechanically synchronised with the main shaft, are operative.

I claim:

1. Anelectric ignition system for an internal combustion engine comprising the armature coil of a magneto arranged to supply energy through separate rectifying means to charge a condenser for subsequent discharge through the primary winding of a transformer, from which the output of the secondary winding is supplied to the fuel ignition means in the engine, and further comprising a single-pole interruptor device in circuit with said coil, arranged sothat opening of said interruptor device results in the charging of said condenser, and subsequent closure of the same interruptor device effects discharge of said condenser through said primary transformer windlng. I

v 2. An electric ignition system for an internal combustion engine comprising the armature coil of a magneto, separate rectifying means in series with said coil, a condenser adapted to be charged by said rectifier output, an output transformer having its primary winding in series with said condenser and its secondary winding adapted for connection to the fuel ignition means in the engine, and circuit make-and-break means, driven with said magneto coil, so arranged that closure of said make-and-break means completes the circult comprising said condenser and said primary transformer winding, thereby discharging the condenser through said primary winding, and

shunt, across said series condenser and primary transformer winding, circuit make-and-break means driven with said magneto coil, which means, when open, ensure charging of said condenser from said rectifying means, and. when closed, discharge said condenser through said primary transformer winding.

4. An electric ignition system for an internal combustion engine comprising the armature coil of a magneto, and in parallel across said coil two lines each incorporating a separate current rectifying device in series with a circuit make-andbreak device, the two rectifying devices being arranged in opposite polarities, and the two makeand-break devices being driven with said coil and arranged so that they open separately during different portions of each complete cycle, and further comprising, in series between the respective Junctions of the said rectifying devices with their associated make-and-break devices, a condenser and the primary winding of an output transformer, of' which the secondary winding is adapted for connection to the fuel ignition means in the engine.

5. An electric ignition system for an internal combustion engine comprising the armature coil of a magneto, and in parallel across said coil two lines each incorporating a separate current rectifying device in series with a circuit make-andbrealr device, the two rectifying devices being arranged in opposite polarities, and the two makeand break devices being driven with said coil and arranged so that they open separately during different portions of each complete cycle, and further comprising two condensers in series with one another between the respective Junctions of the said rectifying means with their associated makeand-break devices, and the primary winding of an output transformer connected between the Junction of saidtwo condensers and the common lead from said two make-and-break devices to the magneto coil.

6. An electric ignition system for an internal combustion engine according to claim 5 wherein the two make-and-break devices are so arranged that one opens just before the other closes and vice versa.

MICHAEL WILLIAM GERALD CHITTY. 

